This paper presents the optimum design for the composite impedance loaded microwave absorbing materials using the genetic algorithm ( GA) .The thickness and the structure of the mult-i layer ferrite absorbing materials and the composite impedance loaded absorbing materials are optimized. The results show that the absorbing performances of the 3-mm-thick and 5-mm-thick microwave absorbing materials increase by 20 % and 10 % respectively with the use of the composite impedance loaded materials. A wider microwave absorbing frequency band is obtained.